The present invention relates generally to cutting elements for rotary driven cylindrical cutters and scarifiers for use in earth working, mining, or other in situ disintegration of hard materials. The invention is particularly directed to such cutting elements for use on a cylindrical surface portion of a rotary driven drum having utility in connection with roadway planing machines, also known as roadway surface reclaiming machines, employed prior to roadway resurfacing.
In general, roadway surface reclaiming machines disclosed in the prior art include a rotary driven cylindrical comminuting drum which acts to scarify and to mine the top portion of an asphaltic road surface in situ. The rotary driven drum typically includes flighting which acts to collect materials mined from the road surface toward a central portion of the drum which material is then removed from the road surface. Usually, the mined material is remixed with additional bituminous material and thereafter redeposited on the roadway as a newly formed smooth asphaltic surface. Examples of prior art apparatus are to be found in U.S. Pat. Nos. 4,139,318, 4,311,284, 4,325,580, 4,480,873 and 5,098,167.
In some prior art devices of this general class, the flighting is formed from a plurality of cutting bit support elements which are mounted on the cylindrical surface of the cutting drum. The cutting bit support members are arranged end-to-end or otherwise in close proximity to form a substantially continuous helical flighting. The top surface of the helical flighting is spaced outward from the cylindrical surface of the drum. The top surface includes forwardly angled openings into which conventional cutting bits are received. The individual cutting bit support members are fixed to the cutting drum cylindrical surface by bolts or other fasteners, or sometimes are welded in place.
In some other prior art devices of this general class, continuous flighting segments, which are adapted to receive cutting bit support members, are welded otherwise fixed to the cylindrical surface of the drum in helical fashion. A plurality of individual cutting bit and support blocks are then fixed to an upper portion of the flighting. Each support block includes a recess for receiving a conventional cutting bit. Each cutting bit constitutes a prong or tine having a tip formed of tungsten carbide or other very hard material adapted to withstand the abrasive character of the roadway being mined by the apparatus.
The hardness of the materials forming the surface of a roadway to be mined can vary substantially depending on the type of aggregate used in its original construction, the age of the surface being mined, weather conditions to which the road has been historically subjected, as well as the current weather conditions at the time of the mining. Many other factors make the life expectancy of the cutting bits unpredictable with cutting bit failure often occurring catastrophically due to rather high value sudden shocks. In the usual course, the failure of individual cutting bits is often not immediately noted thus causing abrasive contact between the cutting bit support member holding the failed cutting bit and the road surface sought to be mined as well as the material removed therefrom by other cutting bits which remain functioning. The cutting bit support members are typically formed of materials, such as steel, which are substantially softer than tungsten carbide and are subject to considerable wear over even short periods of time as the roadway surface reclaiming machine continues to operate. Further, the failure of one bit generally causes adjacent bits to undertake larger than normal mining loads which can lead to premature catastrophic failure of these adjacent bits as well. Such failures demand immediate replacement of the failed cutting bits as well as repair or replacement of the cutting bit supporting members which are damaged as a result of the missing cutting bits. This is a time consuming repair job typically requiring the use of a cutting torch by a welder in the field which results in considerable expense to the machine operator and loss of production time.
Thus, an object of the present invention is to provide a cutting bit holding element designed to hold cutting bits in such a fashion as to preclude substantial abrasive wear of the cutting bit holding element even in the event of catastrophic failure of the cutting bit held by that holding element. An additional object of the present invention is to provide a cutting bit holding element designed to hold cutting bits is such a fashion as to protect the cutting bit holding element even in the event of catastrophic failure of one of the cutting bits.